feat(05-01): extend Progress type with currentForestPage, add paginated renderForestScene

- Add currentForestPage: number field to Progress interface in types.ts
- Export SLOTS_PER_PAGE = 12 constant from scene.ts
- Change renderForestScene signature to accept page: number parameter
- Slice elements by page (start/end = page * SLOTS_PER_PAGE)
- Update navigation UI (forest-nav) after rendering
- Add migrateProgress entry for currentForestPage in app.ts
- Fix Progress object literals in db.test.ts and screens.ts to include new field

src/ui/screens.ts

@@ -83,6 +83,7 @@ export function initWelcomeScreen(
 			totalErrors: 0,
 			errorKeyCounts: {},
 			lastPlayedLevels: [],
+			currentForestPage: 0,
 		};
 		await saveProgress(db, progress);
 		navigateTo("forest");